Cornell University Law School has a great online resource for legal citations.
Introduction to Basic Legal Citation (online ed. 2017) By Peter W. Martin
This work first appeared in 1993. It was most recently revised in December of 2017 to reflect the release of the new sixth edition of the ALWD Guide to Legal Citation. Like all prior revisions this one included a thorough review of the relevant rules of appellate practice of federal and state courts. It takes account of the latest edition of The Bluebook, published in 2015, and The Supreme Court's Style Guide. Point-by-point, it is linked to the free citation guide, The Indigo Book. As has been true of all editions released since 2010, it is also indexed to the The Bluebook and the ALWD Guide. Importantly, however, it documents the many respects in which contemporary legal writing, very often following guidelines set out in court rules or local style guides, diverges from the citation formats specified by those academically produced and focused reference works. The work's current online format, introduced in early 2016, was created with the assistance of students enrolled in a graduate software engineering course at Cornell.
A complementary series of video tutorials offers a quick start introduction to citation of several major categories of legal sources. They may also be useful for review. Currently, the following are available: